This invention concerns propulsion units of marine vehicles, such as ships, submarines or even oil platforms.
These propulsion units, also known by the name “propulsion-oriented drive”, or “POD”, generally include a mobile housing mounted with a pivot link to a hull element of the marine vehicle. For example, the hull element may be placed at the stern or prow of a ship.
In order to provide the pivot link between the mobile housing and the hull element, a rudder rotating bearing can be mounted inside and attached to the hull element.
During the drive unit installation, a direction cone is installed from the inside of the hull element. The upper end of the direction cone is fastened on the rudder bearing. The mobile housing is afterwards introduced from the outside of the hull element, so that its upper end is connected to the lower end of the direction cone. Then, the upper end of the mobile housing is connected to the lower end of the direction cone.
Then, to avoid sea water infiltration inside the hull element and various leaks such as hydraulic fluid or air leaks, sealing gaskets are placed between the hull element and a wall of the drive unit housing, located in its proximity.
Although the use of a direction cone allows sturdy fastening of the drive unit at the rudder bearing, it still has certain disadvantages.
Among these disadvantages, the use of a direction cone results in the rudder bearing position which is relatively far from the sealing gaskets. It leads to the occurrence of a leverage effect when the drive unit is shifting slightly in the vertical plane, when forces are applied to the lower part of the propulsion unit. This leverage effect multiplies the mechanical restrictions applied at the rudder bearing and increases the efforts exerted on the seals.
On the other hand, another disadvantage is that the hull element on which the drive unit is mounted is often directed according to an inclined plane as compared to the horizontal plane of the vehicle. For example, two drive units can be mounted on two elements of the ship hull, on each side and at its stern. In this example, each hull element is locally oriented according to a median inclined plane, as compared with the horizontal plane defined relative to the position of the ship, according to the pitch and roll directions. The two drive units, which include an identical mobile housing, have an unoptimized profile at the hydrodynamic level.
In order to overcome this disadvantage, it might be possible to adapt the housing shape to the shell element on which the drive unit is to be mounted. However, this solution is very expensive both in terms of design as well as manufacturing costs.
Another solution may consist of adding a hydrodynamic adaptation part, also called a “head box”, between the drive unit housing and the hull element. This adaptation part has a hydrodynamic shape adapted to the inclination of the local plane of the hull element compared with a horizontal plane. However, this kind of solution still has some disadvantages, because this adaptation part has an additional hydrodynamic resistance and generates further costs related to manufacturing.